Tidy up checks for missile collision with objects/tiles

This was repeated in multiple places with essentially identical logic. Can expose the existing missiles.cpp function to capture the use in scrollrt.cpp

Source/missiles.cpp

@@ -547,40 +547,21 @@ void CheckMissileCol(Missile &missile, int mindam, int maxdam, bool shift, Point
 			}
 		}
 	}
-	if (dObject[mx][my] != 0) {
-		Object &object = Objects[abs(dObject[mx][my]) - 1];
-		if (!object._oMissFlag) {
-			if (object.IsBreakable()) {
-				BreakObject(-1, object);
-			}
-			if (!nodel)
-				missile._mirange = 0;
-			missile._miHitFlag = false;
+	if (IsMissileBlockedByTile({ mx, my })) {
+		Object *object = ObjectAtPosition({ mx, my });
+		if (object != nullptr && object->IsBreakable()) {
+			BreakObject(-1, *object);
 		}
-	}
-	if (nMissileTable[dPiece[mx][my]]) {
+
 		if (!nodel)
 			missile._mirange = 0;
 		missile._miHitFlag = false;
 	}
+
 	if (missile._mirange == 0 && MissilesData[missile._mitype].miSFX != -1)
 		PlaySfxLoc(MissilesData[missile._mitype].miSFX, missile.position.tile);
 }
 
-/**
- * @brief Could the missile collide with solid objects? (like walls or closed doors)
- */
-bool CouldMissileCollideWithSolidObject(Point tile)
-{
-	int oid = dObject[tile.x][tile.y];
-	if (oid != 0) {
-		oid = abs(oid) - 1;
-		if (!Objects[oid]._oMissFlag)
-			return true;
-	}
-	return nMissileTable[dPiece[tile.x][tile.y]];
-}
-
 void MoveMissileAndCheckMissileCol(Missile &missile, int mindam, int maxdam, bool ignoreStart, bool ifCollidesDontMoveToHitTile)
 {
 	Point prevTile = missile.position.tile;
@@ -633,7 +614,7 @@ void MoveMissileAndCheckMissileCol(Missile &missile, int mindam, int maxdam, boo
 			if (missile._mirange != 0)
 				continue;
 
-			if ((missile._miHitFlag && MissilesData[missile._mitype].MovementDistribution == MissileMovementDistrubution::Blockable) || CouldMissileCollideWithSolidObject(tile)) {
+			if ((missile._miHitFlag && MissilesData[missile._mitype].MovementDistribution == MissileMovementDistrubution::Blockable) || IsMissileBlockedByTile(tile)) {
 				missile.position.traveled = traveled;
 				if (ifCollidesDontMoveToHitTile && missile._mirange == 0) {
 					missile.position.traveled -= incVelocity;
@@ -839,6 +820,21 @@ void SpawnLightning(Missile &missile, int dam)
 
 } // namespace
 
+bool IsMissileBlockedByTile(Point tile)
+{
+	if (!InDungeonBounds(tile)) {
+		return true;
+	}
+
+	if (nMissileTable[dPiece[tile.x][tile.y]]) {
+		return true;
+	}
+
+	Object *object = ObjectAtPosition(tile);
+	// _oMissFlag is true if the object allows missiles to pass through so we need to invert the check here...
+	return object != nullptr && !object->_oMissFlag;
+}
+
 void GetDamageAmt(int i, int *mind, int *maxd)
 {
 	assert(MyPlayerId >= 0 && MyPlayerId < MAX_PLRS);

Source/missiles.h

@@ -168,6 +168,11 @@ void DeleteMissile(int i);
 bool MonsterTrapHit(int m, int mindam, int maxdam, int dist, missile_id t, bool shift);
 bool PlayerMHit(int pnum, Monster *monster, int dist, int mind, int maxd, missile_id mtype, bool shift, int earflag, bool *blocked);
 
+/**
+ * @brief Could the missile collide with solid objects? (like walls or closed doors)
+ */
+bool IsMissileBlockedByTile(Point position);
+
 /**
  * @brief Sets the missile sprite to the given sheet frame
  * @param missile this object

Source/objects.h

@@ -33,6 +33,7 @@ struct Object {
 	bool _oDelFlag;
 	int8_t _oBreak;
 	bool _oSolidFlag;
+	/** True if the object allows missiles to pass through, false if it collides with missiles */
 	bool _oMissFlag;
 	uint8_t _oSelFlag;
 	bool _oPreFlag;

Source/scrollrt.cpp

@@ -106,13 +106,8 @@ bool CouldMissileCollide(Point tile, bool checkPlayerAndMonster)
 		if (dPlayer[tile.x][tile.y] > 0)
 			return true;
 	}
-	int oid = dObject[tile.x][tile.y];
-	if (oid != 0) {
-		oid = abs(oid) - 1;
-		if (!Objects[oid]._oMissFlag)
-			return true;
-	}
-	return nMissileTable[dPiece[tile.x][tile.y]];
+
+	return IsMissileBlockedByTile(tile);
 }
 
 void UpdateMissileRendererData(Missile &m)